Remove all elements from a linked list of integers that have valueval.

Example
Given:1 --> 2 --> 6 --> 3 --> 4 --> 5 --> 6,val= 6
Return:1 --> 2 --> 3 --> 4 --> 5

Credits:
Special thanks to@mithmattfor adding this problem and creating all test cases.

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode removeElements(ListNode head, int val) {
        ListNode dummy = new ListNode(-1);
        dummy.next = head;
        ListNode pre = dummy, cur = head;

        while (cur != null){
            if (cur.val == val){
                pre.next = cur.next;
                cur = cur.next;
            }
            else{
                pre = cur;
                cur = cur.next;
            }
        }

        return dummy.next;
    }
}